Cross-borders smuggling tunnels enable unmonitored movement of people, drugs and weapons and pose a very serious threat to homeland security. Recent advances in strain measurements using optical fibers allow the development of smart underground security fences that could detect the excavation of smuggling tunnels.
Cross-borders smuggling tunnels enable unmonitored movement of people, drugs and weapons and pose a very serious threat to homeland security. Depending on geo-political factors and intended tunnel use, these tunnels range from highly sophisticated infrastructures (for instance at the Mexico-US border, where tunnels are deep and wide and are equipped with communications devices and rail tracks) to shallow hand-dug crawling spaces.
An overview of the prior art can be found in the following articles:    [1] Alsberg, B. K., Woodward, A. M., Winson, M. K., Rowland, J. J., Kell, D. B., 1998. Variable selection in wavelet regression models. Analytica Chimica Acta 368, 29-44.    [2] Yokogawa, 2010. B-OTDR AQ8603: Optical Strain Analyser, http://www.ymtllogin.co.uk/datasheets/aq8603.pdf    [3] Attewell, P. B., Yeates, J., Selby, A. R., 1986. Soil movements induced by tunnelling and their effects on pipelines and structures. Blackie and Son Ltd, London.    [4] Bell, T. H., Barrow, B. J., Miller, J. T., 2001. Subsurface discrimination using electromagnetic induction sensor. IEEE transactions on geoscience and remote sensing 39, 1286-1293    [5] Chandler, R. J., 1988. The in-situ measurements of the undrained shear strength of clays using the field vane. Vane shear strength testing in soils: field and laboratory studies, ASTM STP 1014, A. F. Rochards, Ed., ASTM, Philadelphia, pp. 13-44.    [6] Collar, F., Fenning, P., Mora, C., 2005. Application of drillgole vector magnetic measurements to resolve the position of existing underground structures. NDT&E International 38, 231-236    [7] Debnath, L., 2002. Wavelet transforms and their applications. Birkahuser Publ. Boston.    [8] Depczynski, U., Jetter, K., Molt, K., Niemoller, A., 1999. Quantitative analysis of near infrared spectra by wavelet coefficient regression using a genetic algorithm. Chemometrics and Intelligent Laboratory Systems 47, 179-187.    [9] Ehrentreich, F., 2002. Wavelet transform applications in analytical chemistry. Analytical and Bioanalytical chemistry 372, 115-121.    [10] Ellis, G. A., Peden, I. C., 1997. Cross-borehole sensing: Identification and localization of underground tunnels in the presence of a horizontal stratification. IEEE transactions on geoscience and remote sensing 35, 756-761    [11] Galindez, C. A., Thevenaz, L., 2008. Effect of pulse chirp on distributed Brillouin fiber sensing. 19th International Conference on Optical Fibre Sensors, vol. 7004, p. 70044J-4 SPIE, 2008.    [12] Haykin, S., 1999. Neural networks. A Comprehensive Foundation. Prentice Hall, N.J.    [13] Horiguchi, T., Kurashima, T., Tateda M., 1990. A technique to measure distributed strain in optical fibers. IEEE photonics technology letters 2, 352-354.    [14] Klar, A., Osman, A. S., Bolton, M., 2007. 2D and 3D upper bound solutions for tunnel excavation using ‘elastic’ flow fields. International journal for numerical and analytical methods in geomechanics, 31, 1367-1374. DOI: 10.1002/nag.597    [15] Klar, A., Bennett, P. J., Soga, K., Mair, R. J., Tester, P., Fernie, R., St John, H. D., Torp-Peterson, G., 2006. Distributed strain measurement for pile foundations. Proceedings of the Institution of Civil Engineers-Geotechnical Engineering, 159, 135-144.    [16] Leung, A. K., Chau, F. T., Gao, J. B., Shih, T. M., 1998. Application of wavelet transform in infrared spectrometry: spectral compression and library search. Chemometrics and Intelligent Laboratory Systems 43, 69-88.    [17] Macklin, S. R. 1999 The prediction of volume loss due to tunnelling in overconsolidated clay based on heading geometry and stability number. Ground Engineering, 32(4), 30-33.    [18] Mair, R. J., and Taylor, R. N. (1997). “Bored tunnelling in the urban environment” 14th international conference on soil mechanics and foundation engineering. City: Balkema: Hamburg, pp. 2353-2385.    [19] Mair, R. J., Taylor, R. N., Bracegirdle, A., 1993. Subsurface settlement profiles above tunnels in clays. Geotechnique 43, 315-320.    [20] Marshall, A. M., Mair, R. J., 2008. Centrifuge modelling to investigate soil-structure interaction mechanisms resulting from tunnel construction beneath buried pipelines. Proceedings of the 6th international symposium IS. Shanghai, 10-12 Apr. 2008    [21] Mindlin R. D., 1936. Forces at a Point in the Interior of a Semi-infinite Solid. Physics 7, 195.    [22] Mohamad, H. Bennett, P. J. Soga, K., Klar, A., Pellow, A., 2007. Distributed optical fiber strain sensing in a secant piled wall. ASCE Geotechnical Special Publication 175, pp. 81.    [23] Nikles, M., Thevenaz, L., Robert, P. A. 1997. Brillouin gain spectrum characterization in single mode optical fibers. Journal of light wave technology 15, 1842-1851.    [24] Norville, P. D., Scott, W. R., 2003. Passive detection of buried structures using elastic waves. Proceedings of SPIE—The International Society for Optical Engineering 5090, pp. 142-154    [25] Ohno, H., Naruse, H., Kihara, M., Shimada, A., 2001. Industrial applications of the BOTDR optical fiber strain sensor. Optical fiber technology 7, 45-64    [26] Omnisens, 2005. DiTeSt-STA200 Series: optic fiber distributed sensing system. http://www.omnisens.ch/products/products_dis_ditest_sta200.htm (19/08/05)    [27] Schneider, J., Peden, I. C., 1993. Detection of tunnels in low loss media illuminated by a transient pulse. IEEE transactions on geoscience and remote sensing 31, 503-506    [28] Smith, J., Brown, A., DeMerchant, M. Bao, X., 1999. Simultaneous distributed strain and temperature measurement. Applied optics 38, 5372-5377.    [29] Trygg, J., Wold, S., 1998. PLS regression on wavelet compressed NIR spectra. Chemometrics and Intelligent Laboratory Systems 42, 209-220.    [30] Verruijt, A., Booker, J. R., 1996. Surface settlement due to deformation of a tunnel in an elastic half plane. Geotechnique 46, 753-756.    [31] Vorster, T. E. B., Soga, K., Mair, R. J., Bennett, P. J., Klar, A., Choy, C. K., 2006. The use of optic fiber sensors to monitor pipeline response to tunnelling. GeoCongress 2006: Geotechnical Engineering in the Information Technology Age, pp. 33    [32] Walczak, B., Massart, D. L., 1997. Noise suppression and signal compression using the wavelet packet transform. Chemometrics and Intelligent Laboratory Systems 36, 81-94.    [33] Zeng, X., Bao, X., Chhoa, C. Y., Bremner, T. W., Brown, A. W., DeMerchant, M. D., Ferrier, G., Kalamkarov, A. L., Georgiades, A. V., 2002. Strain measurement in a concrete beam by use of the Brillouin-scattering-based distributed fiber sensor with single-mode fibers embedded in glass fiber reinforced polymer rods and bonded to steel reinforcing bars. Applied optics 41, 5105-5114    [34] Zou, L., Bao, X., Fabien, R., Chen, L. 2006. Distributed Brillouin fiber sensor for detecting pipeline buckling in an energy pipe under internal pressure. Applied optics 45, 3372-3377.
Some of these mentioned above articles are referred to in the specification. For simplicity of explanation an article will be referred using its serial number ([xx]) or the names of its authors and the year of publication (for example—reference [33] can be referred to as Zeng et al., 2002).
Small hand-dug tunnels are routinely excavated along the borders of Israel and the Palestinian-authority and are considered extremely problematic; it is believed by many that the abduction of a Israeli solider by such a tunnel was a key event which led up to the conflicts in Gaza and Lebanon in the summer of 2006.
Various approaches for tunnel detection have been investigated worldwide. Electromagnetic induction sensors can be used to detect tunnels that contain steel (reinforcement rod or rail tracks) ([4], [5]). Listening devices can be used to detect acoustic (mechanical) waves that originate from inside the tunnels ([24]). Finally, the propagation of radar-type waves between two parallel boreholes (transmitting and receiving antennas) can be used to detect tunnels ([27], [10]). Although this method has yielded the most promising results, it requires the constant presence of personnel to move the antennas from one borehole to another.
Even though the results of some of these methods are satisfying for large tunnels, detection of small (<1 m diameter) tunnels remains a major challenge.